This invention relates to a magnetic disk to be loaded in a magnetic disk apparatus, such as a HDD (hard disk drive), for recording information and a method of producing the same.
At present, following the development of the IT (information technology) industry, it is requested to achieve dramatic technical innovation in the information recording technology, in particular, the magnetic recording technology. For example, in the field of a magnetic disk to be loaded in a magnetic disk apparatus, such as a HDD, there is a demand for a technique capable of achieving an information recording density on the order of 40 Gbit/inch2 to 100 Gbit/inch2 or more.
In the magnetic disk apparatus, use has been made of a CSS (Contact Start and Stop) system. In the CSS system, a magnetic head is kept in contact with a contact sliding zone formed on a surface of a magnetic disk when the magnetic disk apparatus is turned off or stopped. In a starting operation, the magnetic head slides on the contact sliding zone in contact therewith to be slightly lifted up. Then, a read or a write operation is started in a read/write zone located outside or inside the contact sliding zone. In the CSS system, the contact sliding zone separate from the read/write zone must be provided on the magnetic disk.
Furthermore, in the CSS system, the surface of the magnetic disk is coated with a protection layer in order to protect the magnetic disk from the magnetic head which slides in contact with the magnetic disk. For example, Japanese Patent Application Publication (JP-A) No. H8-273154 discloses a method of producing a magnetic recording medium, comprising forming a protection layer by sputtering, cleaning each layer formed on a substrate with a cleaning liquid, and drying a surface on which the protection layer is to be formed, thereby improving CSS durability and the like.
In response to a recent demand for an increase in recording density, various approaches have been made in order to achieve an information recording density as high as 100 Gbit/inch2 or more. As one of the approaches, it is required to narrow a gap (magnetic spacing) between a magnetic layer of the magnetic disk and a read/write element of the magnetic head to 20 nm or less so that a spacing loss is decreased and an S/N ratio is improved.
In order to achieve the magnetic spacing of 20 nm or less, the protection layer of the magnetic disk is required to have a thickness as small as 6 nm or less. The magnetic head must have a very low flying height of 12 nm or less. Further, in a recent magnetic disk apparatus, a LUL (Load Unload) system is introduced instead of the CSS system which has been used so far. In the LUL system, the magnetic head is retreated on an inclined support, called a ramp, located outside the magnetic disk when the magnetic disk apparatus is turned off or stopped. In a starting operation, the magnetic head slides from the ramp to an area above the magnetic disk after the rotation of the magnetic disk is started. Then, the magnetic head travels over the magnetic disk in a flying state to carry out a read or a write operation. In a stopping operation, the magnetic head is retreated to the ramp outside the magnetic disk and, thereafter, the rotation of the magnetic disk is stopped. A series of the above-mentioned operations is called a LUL operation.
The LUL system does not require the CSS zone (contact sliding zone for the magnetic head) to be formed on the magnetic disk so that a wide read/write zone is secured on the surface of the magnetic disk as compared with the magnetic disk of the CSS system. Therefore, this system advantageously contributes to a higher recording capacity.
In the LUL system, the magnetic head is not brought into contact with the surface of the magnetic disk, unlike the CSS system. Therefore, it is unnecessary to provide the surface of the magnetic disk with a convex/concave pattern for preventing sucking and sticking of the magnetic head so that the surface of the magnetic disk can be extremely flattened and smoothed. Accordingly, with the magnetic disk of the LUL system, the flying height of the magnetic head can be remarkably lowered as compared with the CSS system. It is therefore possible to achieve a high S/N ratio of a recording signal and to contribute to a higher recording capacity of the magnetic disk apparatus.
Following recent introduction of the LUL system, the flying height of the magnetic head is remarkably lowered. Accordingly, the magnetic disk is required to stably operate even at a very low flying height of 10 nm or less. However, if the magnetic head travels in a flying state over the surface of the magnetic disk at such a very low flying height, there arises a problem of frequent occurrence of a fly stiction defect or a head corrosion defect.
The fly stiction defect is a defect in which the magnetic head is fluctuated in flying position or flying height during traveling in a flying state, often followed by irregular variation in read output. Sometimes, the magnetic head is contacted with the magnetic disk during traveling in a flying state to cause a head crash defect and break the magnetic disk. The head corrosion defect is a defect in which an element portion of the magnetic head is corroded to cause a trouble in the write or the read operation. Sometimes, the write or the read operation is impossible or the corroded element is expanded to damage the surface of the magnetic disk during traveling in a flying state. Occurrence of those defects will significantly deteriorate HDI (Head Disk Interface) reliability of the magnetic head during traveling in a flying state, for example, LUL durability. Further, during traveling in a flying state, the magnetic head may fall onto the surface of the magnetic disk to be sucked and stuck thereto.